The present invention relates to a soldering apparatus of a reflow type and, more particularly, to a soldering apparatus of a reflow type in which electric parts such as chips, temporarily mounted on a printed circuit board are, soldered with solder preforms or solder pastes in a reflow chamber of the soldering apparatus after preheating them in a preheating chamber thereof.
A conventional soldering apparatus of the reflow type is arranged in which printed circuit boards on which chips have been temporarily mounted with solder preforms, solder pastes or adhesives are then exposed to heated air or far infrared rays to fuse or melt the solder preforms or the like, thus soldering the chips on the printed circuit boards.
One conventional soldering apparatus of the reflow type is shown in FIG. 2 in which printed circuit boards 101 with chips 102 temporarily mounted thereon with solder pastes 103 are placed on a belt conveyor 105 of a metal net or mesh being driven by rollers 105a in a direction shown by the arrow A. The soldering apparatus 104 is provided with a first preheating chamber 106 and a second preheating chamber 107 at postions along the direction of conveyance of the belt conveyor 105 and symmetrically and vertically interposing the belt conveyor 105. The first and second preheating chambers 106 and 107 are provided each with an air inlet 106a and 107a and a discharge outlet 106b and 107b, respectively. Air is sucked into the chambers 106 and 107 through the air inlets 106a and 107a, respectively, and the air is heated with a heater 109, such as a sheathed heater or a far infrared rays heater, mounted at the respective discharge outlets 106b and 107b, to temperatures as high as approximately 140.degree. C., for example, below the fusion point of the solder pastes 103 or the like, thus preheating the printed circuit boards 101 being conveyed in the chambers 106 and 107. The preheated printed circuit boards 101 are then conveyed to a reflow chamber 108 in the soldering apparatus 104, which is provided at a discharge exit 108b thereof with a heater 110, such as a sheathed heater or far infrared rays heater. The printed circuit boards 101 are in turn heated with air sucked from an air inlet 108a by the heater 110 at temperatures as high as 215.degree. C., at the fusion point of the solder pastes or the like or higher, thus soldering the chips 102 on the printed circuit boards 101. The heated air is discharged through the discharge outlet 108b. The preheating chambers 106 and 107 and the reflow chamber 108 are further provided each with a fan 111 which is connected through a rotary shaft 112 to each other and to a motor 113. The fans 111 then ventilate heated air in and from the chambers in a direction shown by the arrow B. The soldering apparatus 104 is also provided with a cooling fan 114 for cooling the fused or melted solder pastes 103 to solidify them and ensuring the fixed mounting of the chips 102 to the printed circuit boards 101, and an discharge fan 115 for discharging air inside the soldering apparatus 104.
The heater 109 or 110, such as a sheathed heater or a far infrared rays heater, generates radiant that containing far infrared rays which have the advantage that they are likely to heat even the inside of the chips 102 as compared with a heating system applying a thermal conduction of heated air. It is to be noted, however, that, as the solder pastes 103 have a larger reflectance than the chips 102, the far infrared rays require a longer time for heating the solder pastes 103 than for heating the chips 102, whereby the chips 102 are heated earlier than the solder pastes 103. Consequently, the chips 102 are likely to be damaged.
The heating system using the heater 109 or 110 is more difficult in setting heating requirements than the heating system using heated air because there are many varieties in kinds of printed circuit boards 101 and their sizes.
Furthermore, when a reflecting plate is provided for reflecting heat from the heater 109, 110, the reflecting surface may be coated with flux scattered from the solder pastes 103, worsening the thermal efficiency of the heaters 109, 110.
Accordingly, it is required to block from the printed circuit boards 101 radiant heat including for infrared rays generated from the heater 109, 110.